Multi-electrode implantable stimulator device with a single current path decoupling capacitor

ABSTRACT

Disclosed herein are circuits and methods for a multi-electrode implantable stimulator device incorporating one decoupling capacitor in the current path established via at least one cathode electrode and at least one anode electrode. In one embodiment, the decoupling capacitor may be hard-wired to a dedicated anode on the device. The cathodes are selectively activatable via stimulation switches. In another embodiment, any of the electrodes on the devices can be selectively activatable as an anode or cathode. In this embodiment, the decoupling capacitor is placed into the current path via selectable anode and cathode stimulation switches. Regardless of the implementation, the techniques allow for the benefits of capacitive decoupling without the need to associate decoupling capacitors with every electrode on the multi-electrode device, which saves space in the body of the device. Although of particular benefit when applied to microstimulators, the disclosed technique can be used with space-saving benefits in any stimulator device.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/728,420, filed Jun. 2, 2015 (now U.S. Pat. No. 9,737,713), which is acontinuation of U.S. patent application Ser. No. 13/745,339, filed Jan.18, 2013 (now U.S. Pat. No. 9,072,904), which is a continuation of U.S.patent application Ser. No. 13/012,279, filed Jan. 24, 2011 (now U.S.Pat. No. 8,369,963), which is a continuation of U.S. patent applicationSer. No. 11/550,655, filed Oct. 18, 2006 (now U.S. Pat. No. 7,881,803).Priority is claimed to these applications, and they are incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention relates generally to implantable stimulatordevices, e.g., an implantable pulse generator such as a Bion® device, aSpinal Cord Stimulation (SCS) device, or other type of neuralstimulation devices.

BACKGROUND

Implantable stimulation devices generate and deliver electrical stimulito nerves and tissues for the therapy of various biological disorders,such as pacemakers to treat cardiac arrhythmia, defibrillators to treatcardiac fibrillation, cochlear stimulators to treat deafness, retinalstimulators to treat blindness, muscle stimulators to producecoordinated limb movement, spinal cord stimulators to treat chronicpain, cortical and deep brain stimulators to treat motor andpsychological disorders, occipital nerve stimulators to treat migraineheadaches, and other neural stimulators to treat urinary incontinence,sleep apnea, shoulder sublaxation, etc. The present invention may findapplicability in all such applications, although the description thatfollows will generally focus on the use of the invention within amicrostimulator device of the type disclosed in U.S. Published PatentApplications 2005/0021108, published Jan. 27, 2005; 2005/0057905,published Mar. 17, 2005; and 2004/0059392, published Mar. 25, 2004,which are all incorporated herein by reference in their entireties.However, the present invention also has applicability in otherimplantable stimulator devices, such as Spinal Cord Stimulation (SCS)devices, an example of which can be found in U.S. Pat. No. 6,553,263,which is incorporated herein by reference in its entirety.

Microstimulator devices typically comprise a small generally-cylindricalhousing which carries electrodes for producing a desired electricstimulation current. Devices of this type are implanted proximate to thetarget tissue to allow the stimulation current to stimulate the targettissue to provide therapy for a wide variety of conditions anddisorders. A “microstimulator” in the context of this application meansan implantable stimulator device in which the body or housing of thedevice is compact (typically on the order of a few millimeters indiameter by several millimeters to a few centimeters in length) andusually includes or carries stimulating electrodes intended to contactthe patient's tissue. However, a “microstimulator” may also or insteadhave electrodes coupled to the body of the device via a lead or leads,as shown in U.S. patent application Ser. No. 09/624,130, filed Jul. 24,2000.

Some microstimulators in the prior art contain only one cathodeelectrode. More specifically, in such devices, and referring to FIG. 1,a single anode electrode 14 is provided for sourcing current into aresistance 16, R, i.e., the user's tissue. Typically, a return path forthe current is provided by a single cathode 14′, which could compriseanother electrode on the device, but which might also comprised aportion of the conductive case for the device. Such a device is referredto herein as a “bi-electrode microstimulator,” given its two electrodes14 and 14′. As is known, the anode 14 sources or sinks current using acurrent generator circuit within a programmable Digital-to-AnalogConverter, or “DAC” 20. The cathode 14′ could also be connected to acurrent generator circuit or could simply be tied to a referencepotential. An example of a bi-electrode microstimulator device includesthe Bion® device made by Advanced Bionics Corporation of Sylmar, Calif.

Bi-electrode microstimulators benefit from simplicity. Because of theirsmall size, the microstimulator can be implanted at a site requiringpatient therapy, and without leads to carry the therapeutic current awayfrom the body as mentioned previously. However, such bi-electrodemicrostimulators lack therapeutic flexibility: once implanted, thesingle cathode/anode combination will only recruit nerves in theirimmediate proximity, which generally cannot be changed unless theposition of the device is manipulated in a patient's tissue.

To improve therapeutic flexibility, microstimulators having more thantwo electrodes have been proposed, and such devices are referred toherein as “multi-electrode microstimulators” to differentiate them frombi-electrode microstimulators discussed above. When increasing thenumber of electrodes in this fashion, the electrodes can be selectivelyactivated once the device is implanted, providing the opportunity tomanipulate therapy without having to manipulate the position of thedevice.

Drawings of an exemplary multi-electrode microstimulator 400 are shownin various views in FIGS. 2A-2C. As shown, the device 400 comprises abody or housing 402 which incorporates the power source (battery) andother circuitry needed for the device to function. On the exterior ofthe housing 402 are (in this example) eight conductive connectors 404which are coupled to current generation circuitry in the housing (notshown). In this particular example, and as best shown in FIGS. 2B and2C, a laminate 410 is positioned over the housing so as to bring theconnectors 404 into contact with contact pads 412. The laminate 410 isakin to a printed circuit board and contains conductors 414 whichultimately meet with electrodes 416 designed to directly contact apatient's flesh. Thus, when the housing 402 and laminate 410 are coupledin this manner (FIG. 2C), the result is a multi-electrodemicrostimulator in which the various electrodes 416 are carried by andalong the body of the device. Further details concerning this and otherstructures for a multi-electrode microstimulator are disclosed in thefollowing references, which are incorporated herein in their entireties:U.S. Patent Publication No. 2004/0015205; U.S. Pat. Nos. 7,957,805; and7,920,915. Additionally, a multi-electrode microstimulator need notemploy electrodes on the body 402, and instead or in addition couldcomprise the structure of FIG. 2A with a lead or leads coupling toconnectors 404 (not shown).

An issue concerning the design of any implantable stimulator, andespecially microstimulators of the sort discussed above, involves theuse of decoupling capacitors. One such decoupling capacitor 25, C, isshown in FIG. 1. As is known, decoupling capacitors are useful inimplantable stimulator devices for a number of reasons. First, they canassist in charge recovery after the provision of a stimulation pulse, apoint which is well known in the art and does not require furtherelaboration. Second, they provide additional safety by preventing thedirect injection of current from the current generator circuit (e.g.,inside of DAC 20) to the patient's tissue 16, R.

Examples of the use of decoupling capacitors in the implantablestimulator art are illustrated in FIGS. 3A and 3B. FIG. 3A shows anexample of the use of decoupling capacitors 25 in a Spinal CordStimulation (SCS) device 30, such as the Precision® SCS device marketedby Advanced Bionics Corporation. As shown, this implantable stimulatorcomprises a plurality of electrodes 32, E1-En. Ultimately, a leadextension (not shown) can couple to the electrodes to carry the signalsgenerated by an implantable pulse generator (IPG) to an electrode array(not shown) at the end of a lead. As a result, the electrode array canbe tunneled into position (e.g., along the patient's spinal cord), whilethe IPG is implanted generally at a relative distance (e.g., in thepatient's buttocks).

Associated with each electrode E1-En is a corresponding decouplingcapacitor 25, C1-Cn. In an SCS device 30, the electrodes can beselectively activated, and any activated electrode can be selected as ananode or cathode. Indeed, more than one electrode can be selected as ananode at one time, and more that one electrode can be selected as acathode at one time.

Thus, assume that electrode E2 is selected to act as an anode whileelectrode E4 is selected to act as a cathode as shown in FIG. 3A.Because each electrode E1-En is hardwired with a decoupling capacitorC1-Cn, the resulting current path through the two electrodes E2 and E4includes decoupling capacitors C2 and C4. This assists in chargerecovery at both electrodes, and further provides redundant safety: evenif one of the two capacitors C2 or C4 were to fail, the other wouldprevent the direct injection of current into the tissue R.

This approach of SCS device 30—in which a decoupling capacitor isassociated with each electrode—is generally non-problematic. In an SCSdevice 30, because the IPG is not implanted at the site of requiredtherapy and instead is positioned at a less critical portion of thepatient (e.g., in the buttocks), the IPG can generally be made largerthan can the body of the microstimulators discussed earlier. Forinstance, the IPG used in the SCS device 30 might be disk-shaped with adiameter of a few centimeters and a thickness of several millimeters.There is generally sufficient room in the IPG to accommodate therelatively large decoupling capacitors, C1-Cn. Thus, many currentlymarketed SCS devices 30 employ IPGs having 16 electrodes (17 countingthe case electrode) and 16 corresponding decoupling capacitors (17counting the case).

FIG. 3B illustrates another device 50 in which decoupling capacitorshave been used in the implantable stimulator art, and specificallyillustrates the use of a decoupling capacitor in the bi-electrode Bion®microstimulator device discussed earlier. As noted, bi-electrodemicrostimulator 50 comprises a single cathode 52 and anode 52′. As canbe seen, a single decoupling capacitor C 25 is coupled to the cathode52, and specifically is coupled between the cathode electrode 52 and thecurrent generation circuitry 20. The anode, by contrast, is merelygrounded or tied to a reference potential. Through the use of thedecoupling capacitor, C, the same benefits noted earlier—improved safetyand charge recovery—are had. (However, because only one decouplingcapacitor is provided in the current path there is no redundant safetyas provided by the two decoupling capacitors in the SCS device 30 ofFIG. 3A).

As noted earlier, the body 55 of a bi-electrode microstimulator device50 is very small, meaning there is a reduced volume within the body toaccommodate multiple relatively-large decoupling capacitors 25. However,because such a device traditionally required the use of only a singledecoupling capacitor, space within the body 55 was generally sufficientto accommodate this component.

However, the issue of limited space within the body of a microstimulatorbecomes very significant when a multi-electrode microstimulator iscontemplated. Consider a multi-electrode microstimulator having eightcathodes and one anode (perhaps comprising the device's case). In suchan architecture, and pursuant to the conventional wisdom of the priorart as understood by the Applicants, the microstimulator would need tohave eight decoupling capacitors, one each hard-wired to each electrode.But as noted above, a microstimulator is intended to be quite small.This conflict either limits the number of electrodes a multi-electrodemicrostimulator can carry, or increases body size, neither of which isdesirable.

Accordingly, the implantable stimulator art, and particularly themicrostimulator art, would benefit from the ability to provide multipleelectrodes while still providing sufficient capacitive decoupling thatuses minimal volume inside the device. Embodiments of such a solutionare provided herein.

SUMMARY

Disclosed herein are circuits and methods for a multi-electrodeimplantable stimulator device incorporating one decoupling capacitor inthe current path established via at least one cathode electrode and atleast one anode electrode. In one embodiment, the decoupling capacitoris hard-wired to a dedicated anode on the device. The cathodes areselectively activatable via stimulation switches. In another embodiment,any of the electrodes on the devices can be selectively activatable asan anode or cathode. In this embodiment, the decoupling capacitor isplaced into the current path via selectable anode and cathodestimulation switches. Regardless of the implementation, the techniqueallows for the benefits of capacitive decoupling without the need toassociate decoupling capacitors with every electrode on themulti-electrode device, which saves space in the body of the device.Although of particular benefit when applied to microstimulators, thedisclosed technique can be used with space-saving benefits in anyimplantable stimulator device.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects of the present invention will be moreapparent from the following more particular description thereof,presented in conjunction with the following drawings wherein:

FIG. 1 illustrates the basic electrical components of a microstimulatorin accordance with the prior art.

FIGS. 2A through 2C illustrate various views of a multi-electrodemicrostimulator in accordance with the prior art.

FIGS. 3A and 3B respectively illustrate the stimulation circuitry of aspinal cord stimulator (SCS) system and a bi-electrode microstimulator,and particularly show the decoupling capacitors as used in thosetechniques.

FIG. 4 illustrates an exemplary microstimulator in which the improvedcapacitive decoupling techniques of FIGS. 7-10 can be used.

FIG. 5 illustrates the microstimulator of FIG. 4 and its interactionwith various external components in a microstimulator communicationsystem.

FIG. 6 illustrates several microstimulators of FIG. 4 used together in acommunication network.

FIG. 7 illustrates an embodiment of the invention in which a singledecoupling capacitor is used in a multi-electrode microstimulator.

FIGS. 8A through 8C illustrate further circuitry details andmodifications in a single anode/multi cathode multi-electrodemicrostimulator.

FIGS. 9A through 9C illustrate further circuitry details andmodifications in a single cathode/multi anode multi-electrodemicrostimulator.

FIG. 10 illustrates a multi-electrode microstimulator using a singledecoupling capacitor in an embodiment in which the anodes and/orcathodes are configurable.

FIG. 11 illustrates a schematic of the multi-electrode microstimulatorof FIG. 8A, and shows the provision of the decoupling capacitor inrelation to a main integrated circuit.

DETAILED DESCRIPTION

The following description is of the best mode presently contemplated forcarrying out the invention. This description is not to be taken in alimiting sense, but is made merely for the purpose of describing thegeneral principles of the invention. The scope of the invention shouldbe determined with reference to the claims and their equivalents.

Before discussing the capacitive decoupling aspects that are central tothis disclosure, the circuitry, structure, and function of animplantable stimulator device in which the inventive circuitry can beused is set forth for completeness.

As noted earlier, the disclosed implantable stimulator device maycomprise a microstimulator device, an SCS device, or similar electricalstimulator and/or electrical sensor. However, for convenience, theinventive circuitry is disclosed herein in the context of amicrostimulator. However, it is to be understood that the invention isnot so limited. For example, the present invention may be used as partof a pacemaker, an implantable pump, a defibrillator, a cochlearstimulator, a retinal stimulator, a stimulator configured to producecoordinated limb movement, a cortical or deep brain stimulator, anoccipital nerve stimulator, or in any other stimulator configured totreat urinary incontinence, sleep apnea, shoulder sublaxation, etc.Moreover, the technique can be used in non-medical and/ornon-implantable devices as well.

FIG. 4 illustrates an exemplary implantable microstimulator 100. Asshown, the microstimulator 100 may include a power source 145 such as abattery, a programmable memory 146, electrical circuitry 144, and a coil147. These components are housed within a capsule 202, such as a thin,elongated cylinder or any other shape as best serves a particularapplication. The shape of the capsule 202 may be determined by thestructure of the desired target tissue, the surrounding area, the methodof implantation, the size and location of the power source 145 and/orthe number and arrangement of external electrodes 142. In someembodiments, the volume of the capsule 202 is substantially equal to orless than three cubic centimeters.

The power source 145, e.g., battery 12 of FIG. 1, is configured tooutput a voltage used to supply the various components within themicrostimulator 100 with power. The power source 145 also provides powerfor any stimulation current applied with the microstimulator 100 tonearby tissue, as discussed in the Background section of thisdisclosure. The power source 145 may be a primary battery, arechargeable battery, a capacitor, or any other suitable power source.Systems and methods for recharging the power source 145, where thesource 145 is rechargeable, will be described below.

The coil 147 is configured to receive and/or emit a magnetic field (alsoreferred to as a radio frequency (RF) field) that is used to communicatewith or receive power from one or more external devices that support theimplanted microstimulator 100, examples of which will be describedbelow. Such communication and/or power transfer may include, but is notlimited to, transcutaneously receiving data from the external device,transmitting data to the external device, and/or receiving power used torecharge the power source 145.

The programmable memory unit 146 is used for storing one or more sets ofdata, for example, electrical stimulation parameters as describedfurther below. The programmable memory 146 allows a patient, clinician,or other user of the microstimulator 100 to adjust the stimulationparameters such that the electrical stimulation is at levels that aresafe and efficacious for a particular medical condition and/or for aparticular patient. Electrical stimulation parameters may be controlledindependently. The programmable memory 146 may be any type of memoryunit such as, but not limited to, random access memory (RAM), static RAM(SRAM), EEPROM, a hard drive, or the like.

The electrical stimulation parameters control various parameters of thestimulation current applied to a target tissue including, but notlimited to, the frequency, pulse width, amplitude, burst pattern (e.g.,burst on time and burst off time), duty cycle or burst repeat interval,ramp on time and ramp off time of the stimulation current, etc. Todetermine the strength and/or duration of electrical stimulationrequired to most effectively treat a particular medical condition,various indicators of the medical condition and/or a patient's responseto treatment may be sensed or measured. These indicators include, butare not limited to, muscle or limb activity (e.g., electromyography(EMG)), electrical activity of the brain (e.g., EEG), neurotransmitterlevels, hormone levels, and/or medication levels. In some embodiments,the microstimulator 100 may be configured to change the stimulationparameters in a closed loop manner in response to these measurements.Alternatively, other sensing devices may be configured to perform themeasurements and transmit the measured values to the microstimulator100.

Specific electrical stimulation may have different effects on differenttypes of medical conditions. Thus, in some embodiments, the electricalstimulation may be adjusted by the patient, a clinician, or other userof the microstimulator 100 as best serves a particular medicalcondition. For example, the amplitude of the stimulus current applied toa target nerve may be adjusted to have a relatively low value to targetrelatively large-diameter fibers of the target nerve. Themicrostimulator 100 may also increase excitement of a target nerve byapplying a stimulation current having a relatively low frequency to thetarget nerve (e.g., less than about 100 Hz). The microstimulator 100 mayalso decrease excitement of a target nerve by applying a relatively highfrequency to the target nerve (e.g., greater than about 100 Hz). Themicrostimulator 100 may also be programmed to apply the stimulationcurrent to a target nerve intermittently or continuously.

The microstimulator 100 includes electrodes 142-1 and 142-2 (akin toelectrodes 14 and 14′ of FIG. 1) on the exterior of the capsule 202. Theelectrodes 142 may be disposed at either end of the capsule 202, asillustrated in FIG. 4, or placed along the length of the capsule. Theremay also be more than two electrodes arranged in an array. One of theelectrodes 142 may be designated as a stimulating electrode to be placedclose to the target tissue or treatment site and one of the electrodes142 may be designated as an indifferent electrode (reference node) usedto complete a stimulation circuit. As shown earlier, multiple electrodesmay be positioned along one or more sides of the microstimulatorhousing.

The electrical circuitry 144 is configured to produce electricalstimulation pulses that are delivered to the target nerve via theelectrodes 142. In some embodiments, the microstimulator 100 may beconfigured to produce monopolar stimulation, which may be achieved, forexample, using the stimulator case 202 as an indifferent electrode. Themicrostimulator 100 may alternatively or additionally be configured toproduce bipolar stimulation, which may be achieved, for example, usingone of the electrodes of the electrode array as a cathode and another asan anode.

The electrical circuitry 144 may include one or more microprocessors ormicrocontrollers configured to decode stimulation parameters andgenerate the corresponding stimulation pulses. In some embodiments, themicrostimulator 100 has up to four or more channels and drives up tosixteen electrodes or more. The electrical circuitry 144 may includeadditional circuitry such as capacitors, integrated circuits, resistors,coils, and the like configured to perform a variety of functions as bestserves a particular application.

In the example illustrated in FIG. 4, the microstimulator 100 includestwo or more leadless electrodes 142. However, either or both of theelectrodes 142 may alternatively be located at the ends of short,flexible leads. The use of such leads permits, among other things,electrical stimulation to be directed to targeted tissue(s) a shortdistance from the surgical fixation of the bulk of the device 100 at amore surgically convenient site. This minimizes the distance traversedand the surgical planes crossed by the device 100 and any lead(s).

The external surfaces of the microstimulator 100 are preferably composedof biocompatible materials. For example, the capsule 202 may be made ofglass, ceramic, metal, or any other material that provides a hermeticpackage that excludes water vapor but permits passage of electromagneticfields used to transmit data and/or power. The electrodes 142 may bemade of a noble or refractory metal or compound, such as platinum,iridium, tantalum, titanium, titanium nitride, niobium or alloys of anyof these, to avoid corrosion or electrolysis which could damage thesurrounding tissues and the device.

The microstimulator 100 may also include one or more infusion outlets201, which facilitate the infusion of one or more drugs into the targettissue. Alternatively, catheters may be coupled to the infusion outlets201 to deliver the drug therapy to target tissue some distance from thebody of the microstimulator 100. If the microstimulator 100 isconfigured to provide a drug stimulation using infusion outlets 201, themicrostimulator 100 may also include a pump 149 that is configured tostore and dispense the one or more drugs.

Of course, the microstimulator 100 of FIG. 4 is illustrative of manytypes of microstimulators that may be used to apply stimulation totarget tissue to treat a particular medical condition. Other types ofmicrostimulators, as well as details concerning microstimulatormanufacture and operation can be found in the various patent documentsincorporated by reference elsewhere in this disclosure.

Turning to FIG. 5, the microstimulator 100 is illustrated as implantedin a patient 150, and further shown are various external components thatmay be used to support the implanted microstimulator 100. For example,an external battery charging system (EBCS) 151 may provide power used torecharge power source 145 (FIG. 4) via an RF link 152. As is known inthe art, the RF link comprises electromagnetic energy which energizesthe coil 147 (FIG. 4) through the patient 150's tissue, and which isrectified, filtered, and used to recharge the power source 145.

Other external components such as a hand held programmer (HHP) 155,clinician programming system (CPS) 157, and/or a manufacturing anddiagnostic system (MDS) 153 may be used to activate, deactivate,program, and test the microstimulator 100 via one or more RF links 154,156. Thus, one or more of these external devices 153, 155, 157 may alsobe used to control the microstimulator 100 to provide stimulationelectrical pulses necessary to treat a particular medical condition, andmay be used to provide or update the stimulation parameters and otherdata stored in the programmable memory (146, FIG. 4) of themicrostimulator 100. Furthermore, the external devices 153, 155, 157 maycommunicate with each other. For example, the CPS 157 may communicatewith the HHP 155 via an infrared (IR) link 158 or via any other suitablecommunication link. Likewise, the MDS 153 may communicate with the HHP155 via an IR link 159 or via any other suitable communication link.

Additionally, the microstimulator 100 may report its status or variousother parameters to any of the external devices via the two-way RF links152, 154, and 156. For example, once the logic circuitry detects thatthe power source 145 is fully charged, the coil 147 (FIG. 4) is used tosignal that fact back through the RF link to the EBCS 151 so thatcharging can cease. Likewise, once stimulation parameters are sent fromeither of the HHP 155 or the MDS 153, acceptance of those parameters canbe reported back to those devices, and/or the actual parameters can bereported back as a double check.

The HHP 155, MDS 153, CPS 157, and EBCS 151 are merely illustrative ofthe many different external components that may be used in connectionwith the microstimulator 100. Furthermore, it will be recognized thatthe functions performed by the HHP 155, MDS 153, CPS 157, and EBCS 151may be performed by combination devices or a single external device. Oneor more of these external devices may be embedded in a seat cushion,mattress cover, pillow, garment, belt, strap, pouch, or the like, so asto be conveniently placed near the implanted microstimulator 100 when inuse.

With the implantable and external components of the system understood,an exemplary method in which the microstimulator 100 can be used totreat a particular medical condition is briefly illustrated. First, themicrostimulator 100 is implanted so that its electrodes (142, FIG. 4)are coupled to or located near a target tissue. The microstimulator 100is programmed with stimulation parameters to apply at least one stimulusto the target tissue. When the patient desires treatment with theprogrammed stimulation parameters, the patient sends a command to themicrostimulator 100 (e.g., via a remote control) and the microstimulator100 in turn delivers the prescribed stimulation. The microstimulator 100may be alternatively or additionally configured to automatically applythe electrical stimulation in response to sensed indicators of theparticular medical condition. To cease electrical stimulation, thepatient may turn off the microstimulator 100 (again, via the remotecontrol). When necessary, the EBCS 151 is activated to recharge thepower source 145 as described above, and this can occur at convenientintervals for the patient 150, such as every night.

In some therapies, it may be desirable to employ more than onemicrostimulator 100, each of which could be separately controlled bymeans of a digital address. This allows multiple channels and/ormultiple patterns of electrical stimulation to be used as is efficaciousfor certain medical conditions. For instance, as shown in the example ofFIG. 6, a first microstimulator 100 implanted in a patient 150 providesa stimulus to a first location; a second microstimulator 100′ provides astimulus to a second location; and a third microstimulator 100″ providesa stimulus to a third location. As mentioned earlier, the implanteddevices may operate independently or may operate in a coordinated mannerwith other implanted devices or other devices external to the patient'sbody. That is, an external controller 250 (indicative of any of theexternal components of FIG. 5 or combinations of those components) maybe configured to control the operation of each of the implanted devices100, 100′, and 100″ via RF links 262-264. In some embodiments, oneimplanted device, e.g. microstimulator 100, may control or operate underthe control of another implanted device(s), e.g., microstimulator 100′and/or microstimulator 100″, via RF links 265-267.

As a further example of multiple microstimulators 100 operating in acoordinated manner, the first and second microstimulators 100, 100′ ofFIG. 6 may be configured to sense various indicators of a particularmedical condition and to transmit the measured information to the thirdmicrostimulator 100″. The third microstimulator 100″ may then use themeasured information to adjust its stimulation parameters and to applymodified electrical stimulation to the target tissue accordingly.

Alternatively, the external device 250 may be configured to sensevarious indicators of a patient's condition. The sensed indicators canthen be transmitted to one or more of the implanted microstimulatorswhich may adjust stimulation parameters accordingly. In other examples,the external controller 250 may determine whether any change tostimulation parameters is needed based on the sensed indicators. Theexternal device 250 may then signal a command to one or more of themicrostimulators to adjust stimulation parameters accordingly.

With the basic structure and function of a microstimulator now in hand,focus now shifts to a detailed description of the capacitive decouplingtechniques that are the focus of this disclosure.

As noted earlier, an issue in multi-electrode microstimulators involvesthe electrode decoupling capacitors. Such capacitors are relativelylarge and take up significant space within the body of themicrostimulator. Thus, a problem is presented when a microstimulator hasmultiple electrodes, because conventional wisdom suggests a need formultiple decoupling capacitors.

An embodiment of the invention contrary to such conventional wisdom isshown in FIG. 7, and in further circuitry detail in FIG. 8A. Shown is amulti-electrode microstimulator device 300 having a plurality ofelectrodes 320, 322 a-n, which electrodes can be carried on its body 305and/or on a lead(s). (For simplicity, in the embodiments as depicted inFIGS. 7-11, the electrodes are shown as carried on the body and withoutthe use of leads). In this embodiment, the electrodes are split betweena plurality (“n”) of cathodes 322 a-n (e.g., eight cathodes) and adedicated anode 320, which like the cathodes can be carried on the bodyor lead-coupled to the body.

Despite the provision of a plurality of cathodes 322 a-n, note that theembodiment provides a single decoupling capacitor 302. In thisembodiment, a first plate 302 a of the capacitor is hardwired to thededicated anode 320, while the second plate 302 b essentiallycommunicates with the compliance voltage (V+) which in conjunction withthe current generation circuitry 333 sets the current in the DAC 20.However, intervening between the second plate 302 b and the compliancevoltage V+ is a switch whose functions will be explained shortly.

Two types of switches are set forth in the embodiment of FIG. 8A:stimulation switches 310 and 312 a-n, and recovery switches 314 and 316a-n. Both types of switches are apparent on the anode 320 and on thecathodes 322 a-n. Thus, the anode path comprises a stimulation switch310 and a recovery switch 314. Each of the cathode paths similarlycomprises a stimulation switch 312 a-n and a recovery switch 316 a-n.

During provision of a stimulation pulse, the anode's stimulation switch310 is closed, as is one of the cathode stimulation switches 312 a-n.Which cathode stimulation switch is selected depends on which cathodehas been deemed most appropriate for a given patient's therapy. Forexample, suppose experimentation reveals that a given patient feels thebest relief when cathode 322 b is activated. In this case, during activestimulation, switch 312 b is closed, as well as switch 310 in the anodepath. Other cathode stimulation switches 312 a and 312 c-312 n remainopen. The result is a current path through the anode stimulation switch310, through anode 320, through the patient's tissue (not shown),through cathode 322 b, through the cathode stimulation switch 312 bassociated with cathode 322 b, and ultimately to ground as dictated bycurrent generation circuitry 333 in the DAC 20. Notice that thedecoupling capacitor 302 is present in the anode path (and hence in theoverall current path). Thus, the benefits of capacitive decouplingdiscussed earlier (charge recovery; safety) are preserved in thedisclosed embodiment.

Of course, it should be noticed that any of the cathodes 322 could bechosen via their associated stimulation switches 312. However, becausethe decoupling capacitor 302 is dedicated to the anode path, capacitivedecoupling and its benefits are maintained, even though only onedecoupling capacitor is used. This is a significant shift inconventional wisdom in the art, which suggests the use of ‘n’ differentdecoupling capacitors.

The recovery switches 314 and 316 a-n are activated at some point afterprovision of a stimulation pulse, and have the goal of recovering anyremaining charge left on the decoupling capacitor 302 and in thepatient's tissue. Thus, after a stimulation pulse, the recovery switches314 and 316 a-n are closed. (Actually, only one of the cathode recoveryswitches 316 a-n need be closed, preferably the switch corresponding tothe previously-active cathode 322 a-n. However, it is harmless andsimple to close all of switches 316 a-n during recovery). Closure ofthese switches places the same reference voltage on each plate of thedecoupling capacitor 302, thus removing any stored charge. In oneembodiment, for convenience, the reference voltage used is the batteryvoltage, Vbat, although any other reference potential could be used.Thus, Vbat is placed on the second plate 302 b of decoupling capacitor302 via anode recovery switch 314, and is likewise placed on the firstplate 302 a through the patient's tissue via cathode recovery switches316 a-n.

While the use of recovery switches 314, 316 a-n has been described, suchswitches are not necessary to all useful embodiments of the invention,especially if charge recovery is not a significant concern in aparticular application, or if other means are used to ensure chargerecovery. In short, the recovery switches 314, 316 a-n may be dispensedwith in other useful embodiments of the invention. For example, andalthough not shown in FIG. 8A for simplicity, it can be beneficial toprovide high-resistance “bleeder” resistors in parallel across therecovery switches 314 and 316 a-n to allow charge to bleed off thecapacitor 302 very slowly. This ensures that the capacitor 302 caneventually be discharged during all conditions, such as during periodsof no stimulation. Of course, such bleeder resistors should be of highenough resistance to not significantly shunt the operation of theswitches 314 and 316 a-n during normal operation. In the embodiment ofFIG. 8A, bleeder transistors, if used, could be present across the anoderecovery switch 314 and at least one of the cathode recovery switches316 a-n.

The stimulation switches 310 and 312 a-n and recovery switches 314 and316 a-n can comprise any switching structure or circuit such astransistors, transmission gates, etc. One embodiment showing circuitrythat may be used for these switches is shown to the left of FIG. 8A.Thus, transistors are used for the stimulation switches 310, 312 a-n,although a P-channel is used for the anode path switch 310, whileN-channels are used for the cathode path switches 312 a-n, which issensible given the relative voltages present at those locations. Therecovery switches 314 and 316 a-n comprises transmission gates. Thecontrol (gate) signals for these various switches (Rec/Rec*, Stim_Anode,Stim_Cathode_n) are generated by a suitable microcontroller or any otherfrom of digital controller present in the microstimulator 300 (notshown).

As shown in FIG. 8A, the current generation circuitry 333 is placed inthe cathode path, i.e., in the opposite path from where the decouplingcapacitor 302 is placed. However, as shown in FIG. 8B, the currentgeneration circuitry 333 can also be placed in the anode path, i.e., inthe same path where the decoupling capacitor 302 is placed. Indeed,FIGS. 8A and 8B can essentially be combined such that current generationcircuitry 333 appears in both the cathode and anode paths. Moreover, thecurrent generation circuitry 333 as shown in the cathode path can bedistributed such that each cathode has its own dedicated andprogrammable current generation circuitry 333 a-n, as shown in FIG. 8C.

Moreover, and as shown in FIGS. 9A through 9C, the techniques disclosedcan be employed to the case of a single cathode/multiple anodemicrostimulator 300′. Because these figures largely correspond to FIGS.8A through 8C and should be clear to those of skill in the art, they arenot further discussed.

As discussed above, in the embodiments of FIGS. 8A through 9C, an anodeor cathode is specifically dedicated on the multi-electrodemicrostimulator. However, in other embodiments, it may be desirable tomake a multi-electrode microstimulator more flexible. For example, ifthe multi-electrode microstimulator has eight electrodes, it may bedesirable to designate any of the eight electrodes as the anode and anyof the electrodes as the cathode. Such a design would provide the utmostflexibility for the multi-electrode microstimulator to recruit targetnerves so as to best benefit the patient.

FIG. 10 illustrates an embodiment of a multi-electrode microstimulator350 providing such flexibility. Much of the circuitry in FIG. 10 is thesame as that disclosed with respect to FIG. 8A, and so discussion ofthat circuitry is not repeated here. For example, optional recoveryswitches 314 and 316 a-n and use of a single decoupling capacitor 302are again utilized in device 350.

However, some differences are apparent. First, consistent with theconfigurable nature of the device 350, the electrodes 340 a-n are notdefined or pre-designated as anodes or cathodes; instead, any of theelectrodes 340 a-n can be programmed to function as either the anode orthe cathode. Second, in addition to cathode stimulation switches 312a-n, anode selection switches 330 a-n (e.g., implemented as P-channeltransistors) are present between the first plate 302 a of the decouplingcapacitor 302 and the electrodes; by comparison, the first plate washard wired in the embodiment of FIG. 8A. Using the cathode selectionswitches 312 a-n and the anode selection switches 330 a-n, the user mayspecify which of the ‘n’ electrodes will comprise the anode and thecathode. For example, the electrode E2 may be selected as the anode byclosing anode selection switch 330 b, while electrode E1 may be selectedas the cathode by closing cathode selection switch 312 a. At the sametime, switches 330 a and 312 b would be kept open. In short, switches312 a-n and 330 a-n comprise a switching matrix to allow any of theplurality of the electrodes to act as either the anode or the cathode.

Regardless of what electrode is selected as the anode or cathode, thedecoupling capacitor 302 remains in the established current path.Accordingly, the benefits to capacitive decoupling discussed earlier areonce again preserved in the embodiment of device 350. At the same time,only one decoupling capacitor 302 is needed to service the multipleelectrodes, thus saving room within the body 305 of the microstimulator350.

It should be noted that during current recovery, one or all of anodestimulation switches 330 a-n would need to be closed as well as therecovery switches 314 and 316 a-n to short the first 302 a and second302 b plates of the decoupling capacitor.

The electrode configurable microstimulator 350 of FIG. 10 can of coursealso be modified in the various ways illustrated in FIGS. 8A-9C. Forexample, and as shown in FIGS. 8C and 9C, multiple current generationcircuits could be utilized.

A circuit schematic showing an implementation of theone-decoupling-capacitor technique disclosed herein is shown in FIG. 11.As shown, the multi-electrode microstimulator 300 may contain a mainintegrated circuit (IC) 500, which could include the device's logicfunctions, current generation and monitoring circuitry, etc. Coupled tothe IC 500 are shown various exemplary discrete components relevant torectification and tuning of RF communications (left side), and theelectrodes (right side). One such discrete component comprises thesingular decoupling capacitor C 302 that has been a focal point of thisdisclosure. However, it should be noted that other discrete components,and specifically other discrete capacitors, may also be present. Forexample, capacitors may be provided for compliance voltage stabilization(502) and for tuning the telemetry (RF link) coil 147 (504).

Embodiments of the invention using a single decoupling capacitor 302 inan implantable stimulator device have been discussed as particularlyuseful in the context of multi-electrode microstimulators. As noted,such devices have relatively small body volumes, and hence greatlybenefit from the requirement to accommodate only one capacitor. However,the inventive aspects of this disclosure can also be used in implantablestimulator devices that do not comprise microstimulators. For example,in the SCS device 30 discussed earlier (FIG. 3A), it was noted that thebody 35 of such a device may have room for decoupling capacitorsdedicated to each electrode. However, that body 35 can be made evensmaller using the disclosed techniques. For example, using embodimentsof the invention, the number of decoupling capacitors C1-Cn could bereduced to one in an SCS device 30.

Alternatively, it should be noted that the disclosed techniques may notnecessary result in the use of a single decoupling capacitor within agiven device body, and instead the techniques may merely be implementedto reduce the number of decoupling capacitors within the device body.Consider the eight-electrode microstimulator of FIG. 8A. If desired, thecircuitry as disclosed can be used for four electrodes, which circuitrycan then be duplicated to form two sets of circuitry suitable forserving all eight electrodes. In this case, each set could include onedecoupling capacitor 302, and thus there could be two capacitors, onefor each set, with one capacitor to optimize the four electrodes in itsset pursuant to the techniques disclosed herein. In this case, thedevice body would need to house only two decoupling capacitors. This isnot as optimal as earlier embodiments employing a single decouplingcapacitor from a space perspective, but it does mark an improvementcompared to the conventional wisdom, which would employ the use of eightcapacitors. Additionally, if the electrodes are grouped in sets in thismanner, additional flexibility could be provided, such as the ability tosimultaneously designate two cathodes (one in each set) and two anodes(again, one in each set).

While the invention herein disclosed has been described by means ofspecific embodiments and applications thereof, numerous modificationsand variations could be made thereto by those skilled in the art withoutdeparting from the literal and equivalent scope of the invention setforth in the claims.

What is claimed is:
 1. A stimulator device, comprising: a body for thedevice comprising a case; a first plurality of electrode nodes, whereinthe first plurality of electrode nodes are each configured to connect toone of a first plurality of electrodes configured to contact a tissue ofa patient; and a first set of circuitry, comprising: a first switchmatrix configured to select any of the first plurality of electrodenodes as a first active anode and any of the first plurality ofelectrode nodes as a first active cathode to establish a first currentpath, and a first decoupling capacitor, wherein each first current pathincludes the first decoupling capacitor; wherein the first switch matrixis not configured to connect any of the first plurality of electrodenodes to a decoupling capacitor other than the first decouplingcapacitor.
 2. The device of claim 1, wherein the first plurality ofelectrodes are carried on the body.
 3. The device of claim 1, furthercomprising a lead coupled to the body, wherein the first plurality ofelectrodes are carried on the lead.
 4. The device of claim 1, whereinthe body is configured to be implantable in the patient.
 5. The deviceof claim 1, further comprising recovery circuitry for shunting bothplates of the first decoupling capacitor to a common potential.
 6. Thedevice of claim 1, wherein the first switch matrix comprises a pluralityof anode switches and a plurality of cathodes switches, wherein each ofthe plurality of first electrode nodes is coupled to one anode switchand to one cathode switch.
 7. The device of claim 1, wherein the firstplurality of electrodes comprise all of the electrodes configured tocontact the tissue of the patient.
 8. The device of claim 1, wherein thefirst decoupling capacitor is coupled between a first reference voltageand the first switch matrix.
 9. The device of claim 1, furthercomprising: a second plurality of electrode nodes, wherein the secondplurality of electrode nodes are each configured to connect to one of asecond plurality of electrodes that contact a tissue of a patient; and asecond set of circuitry, comprising: a second switch matrix andconfigured to select any of the second plurality of electrode nodes as asecond active anode and any of the second plurality of electrode nodesas a second active cathode to establish a second current path, and asecond decoupling capacitor, wherein each second current path includesthe second decoupling capacitor; wherein the second switch matrix is notconfigured to connect any of the second plurality of electrode nodes toa decoupling capacitor other than the second decoupling capacitor.
 10. Astimulator device, comprising: a body for the device comprising a case;a first plurality of electrode nodes, wherein the first plurality ofelectrode nodes are each configured to connect to one of a firstplurality of electrodes configured to contact a tissue of a patient; anda first set of circuitry, comprising: a first reference voltage, a firstdecoupling capacitor, a first switch matrix coupled between the firstreference voltage and the first plurality of electrode nodes, whereinthe first switch matrix is configured to select any of the firstplurality of electrode nodes as a first active anode, and wherein thefirst decoupling capacitor is coupled between the first referencevoltage and the first switch matrix, a second reference voltage, and asecond switch matrix coupled between the second reference voltage andthe first plurality of electrode nodes, wherein the second switch matrixis configured to select any of the first plurality of electrode nodes asa first active cathode, and wherein no decoupling capacitor is coupledbetween the second reference voltage and the second switch matrix. 11.The device of claim 10, wherein the first plurality of electrodes arecarried on the body.
 12. The device of claim 10, further comprising alead coupled to the body, wherein the first plurality of electrodes arecarried on the lead.
 13. The device of claim 10, wherein the body isconfigured to be implantable in the patient.
 14. The device of claim 10,further comprising recovery circuitry for shunting both plates of thefirst decoupling capacitor to a common potential.
 15. The device ofclaim 10, wherein the first plurality of electrodes comprise all of theelectrodes configured to contact the tissue of the patient.
 16. Thedevice of claim 10, further comprising: a second plurality of electrodenodes, wherein the second plurality of electrode nodes are eachconfigured to connect to one of a second plurality of electrodesconfigured to contact a tissue of a patient; and a second set ofcircuitry, comprising: a second decoupling capacitor, a third switchmatrix coupled between the first reference voltage and the secondplurality of electrode nodes, wherein the third switch matrix isconfigured to select any of the second plurality of electrode nodes as asecond active anode, and wherein the second decoupling capacitor iscoupled between the first reference voltage and the second switchmatrix, and a fourth switch matrix coupled between the second referencevoltage and the second plurality of electrode nodes, wherein the fourthswitch matrix is configured to select any of the second plurality ofelectrode nodes as a second active cathode, and wherein no decouplingcapacitor is coupled between the second reference voltage and the fourthswitch matrix.
 17. The device of claim 10, further comprising firstcurrent generation circuitry between the first reference voltage and thefirst switch matrix.
 18. The device of claim 10, further comprisingsecond current generation circuitry between the second reference voltageand the second switch matrix.
 19. The device of claim 10, furthercomprising first current generation circuitry between the firstreference voltage and the first switch matrix, and second currentgeneration circuitry between the second reference voltage and the secondswitch matrix.
 20. The device of claim 10, wherein the first switchmatrix is not configured to connect any of the first plurality ofelectrode nodes to a decoupling capacitor other than the firstdecoupling capacitor.
 21. The device of claim 10, wherein the secondswitch matrix is not configured to connect any of the first plurality ofelectrode nodes to a decoupling capacitor.